The present invention relates to the data collection systems for collection of data, which is picked up at a plurality of different sites, is transferred to a central or base station for storage, display for data processing purposes, and particularly which pickup of the data is carried out by portable data units which may be located at different sites remote from the base station and communicate therewith by wireless exchange of messages, such as by radio transmissions.
The invention is especially suitable for the collection of data read by bar code scanners (sometimes bar code readers) which may move from place to place so as to read labels on items at different locations, for example, in a warehouse or factory. The invention provides an improved communications protocol which is especially adapted for wireless collection of data from bar code scanners or other data collection terminals. The protocol may also be suitable for use with other communication networks where robust reliable and effective data communication is desired.
In order to provide for robustness in communication of messages, there is networking multiplexing and communication modes have been proposed. One proposal, which has been made for collection of data from remote bar code scanners by radios involved, involve selective, interactive communication between a base station and the remote units. Spread spectrum techniques have been used together with protocols for sensing potential collisions or simultaneous communication between the central station and different units. See Tymes, U.S. Pat. No. 5,029,183 issued Jul. 2, 1991 and various patents which are divisions continuations, etc. therefrom, such as U.S. Pat. No. 5,157,687, issued Oct. 20, 1992 and U.S. Pat. No. 5,280,498 issued Jan. 18, 1994.